The microtubule cytoskeleton is essential for cellular processes such as mitosis, organelle transport, and cell polarity. The key organizer of microtubules is the microtubule organizing center (MTOC). All MTOCs are composed of multi-protein complexes and share three general properties: a) They nucleate microtubules. b) They arrange the microtubules into functional patterns. And c) They attach the microtubules to their proper organelle targets. In recent years the molecules that are localized to the centrosome, the primary MTOC in animal cells, have been catalogued and much progress has been made in understanding the mechanism by which the g-tubulin ring complex (g-TuRC) located at the centrosome nucleate microtubules. However, most cytoplasmic g-TuRCs are not located at the centrosome, and their cellular functions are unknown. Furthermore, while the canonical centrosome arranges radial arrays of microtubules which are attached to the nucleus, many highly differentiated cell types - neurons, myotubes, and polarized epithelial cells - have linear arrays of microtubules which are not attached to the nucleus. The mechanisms which generate linear arrays of microtubules are unknown and is the subject of this research proposal. My lab recently identified ase1+ and mto2+, whose gene products localize to the three different MTOCs. Aselp plays key roles in linear arrangement of microtubules; and mto2p plays key roles in microtubule nucleation. And we will now focus on dissecting the roles of aselp and mto2p in organizing linear arrays of microtubules. This proposal will combine yeast genetics, biochemistry, and molecular biology with quantitative optical microscopy methods such as FRAP and optical tweezers to study the role of aselp and mto2p in organizing linear microtubule arrays. Our studies will provide new insights into the molecular mechanism which underlie the biogenesis of linear microtubule arrays. Furthermore, evolutionary conservation will make our findings in fission yeast highly relevant to our understanding of similar conserved structures in human cells, and may contribute to our understanding of disease arising from the pathology of MTOC formation and function.